The present invention relates to a sliding element for a shoe sole, in particular a shoe sole with a sliding element that provides cushioning to the shoe in three dimensions.
Shoe soles should primarily meet two requirements. First, they should provide good friction with the ground. Second, they should sufficiently cushion the ground reaction forces arising during a step cycle to reduce the strains on the wearer""s muscles and bones. These ground reaction forces can be classified into three mutually orthogonal components, i.e., a component occurring in each of the X-direction, the Y-direction, and the Z-direction. The Z-direction designates a dimension essentially perpendicular (or vertical) to the ground surface. The Y-direction designates a dimension essentially parallel to a longitudinal axis of a foot and essentially horizontal relative to the ground surface. The X-direction designates a dimension essentially perpendicular to the longitudinal axis of the foot and essentially horizontal relative to the ground surface.
The largest ground reaction force component typically occurs in the Z-direction. Studies have shown that peak forces of approximately 2000 N may occur in the Z-direction during running. This value is about 2.5 to 3 times the body weight of a typical runner. Accordingly, in the past, the greatest attention was directed to the strains of the muscles and the bones caused by this force component and the many different arrangements for optimizing the cushioning properties of a shoe in the Z-direction.
Ground reaction forces, however, further include noticeable force components in the X-direction and in the Y-direction. Measurements have shown that forces of approximately 50 N in the X-direction and of approximately 250 N in the Y-direction may occur in a heel area during running. During other sports, for example lateral sports such as basketball or tennis, forces of up to 1000 N may occur in a forefoot area in the X-direction during side cuts, impact, and push off.
The aforementioned horizontal forces in the X- and Y-directions are one reason why running on an asphalt road is considered uncomfortable. When the shoe contacts the ground, its horizontal movement is essentially completely stopped within a fraction of a second. In this situation, the horizontally effective forces, i.e., the horizontal transfer of momentum, are very large. This is in contrast to running on a soft forest ground, where the deceleration is distributed, over a longer time period due to the reduced friction of the ground. The high transfer of momentum can cause premature fatigue of the joints and the muscles and may, in the worst case, even be the reason for injuries.
Further, many runners contact the ground with the heel first. If viewed from the side, the longitudinal axis of the foot is slightly inclined with respect to the ground surface (i.e., dorsal flexion occurs). As a result, a torque, which cannot be sufficiently cushioned by compression of a sole material in the Z-direction alone, is exerted on the foot during first ground contact. This problem becomes worse when the runner runs on a downhill path, since the angle between the shoe sole and the ground increases in such a situation.
In addition, road surfaces are typically cambered for better water drainage. This leads to a further angle between the sole surface and the ground plane. Additional loads, caused by a torque on the joints and the muscles, are, therefore, created during ground contact with the heel. With respect to this strain, the compression of the sole materials in the Z-direction alone again fails to provide sufficient cushioning. Furthermore, during trail running on soft forest ground, roots or similar bumps in the ground force the foot during ground contact into an anatomically adverse inclined orientation. This situation leads to peak loads on the joints.
There have been approaches in the field to effectively cushion loads that are not exclusively acting in the Z-direction. For example, International Publication No. WO98/07343, the disclosure of which is hereby incorporated herein by reference in its entirety, discloses 3D-deformation elements that allow for a shift of the overall shoe sole with respect to a ground contacting surface. This is achieved by a shearing motion of an elastic chamber, where the walls are bent to one side in parallel so that the chamber has a parallelogram-like cross-section, instead of its original rectangular cross-section, under a horizontal load.
A similar approach can be found in U.S. Pat. No. 6,115,943, the disclosure of which is hereby incorporated herein by reference in its entirety. Two plates interconnected by means of a rigid linkage below the heel are shifted with respect to each other. The kinematics are similar to International Publication No. WO98/07343, i.e., the volume defined by the upper and lower plate, which is filled by a cushioning material, has an approximately rectangular cross-section in the starting configuration, but is transformed into an increasingly thin parallelogram under increasing deformation.
One disadvantage of such constructions is that cushioning is only possible along a single path, as predetermined by the mechanical elements. For example, the heel unit disclosed in U.S. Pat. No. 6,115,943 allows only a deflection in the Y-direction, which is simultaneously coupled to a certain deflection in the Z-direction. With respect to forces acting in the X-direction, the sole is substantially rigid. Another disadvantage of such constructions is that the horizontal cushioning is not decoupled from the cushioning in the Z-direction. Modifications, of the material or design parameters for the Z-direction can have side effects for the horizontal directions and vice versa. Accordingly, the complex multi-dimensional loads occurring during the first ground contact with the heel, in particular in the above discussed situations with inclined road surfaces, cannot be sufficiently controlled.
Further, U.S. Pat. No. 5,224,810, the disclosure of which is also hereby incorporated herein by reference in its entirety, discloses dividing the overall sole of a shoe into two wedge-like halves which are shifted with respect to each other, wherein the movement is limited to the X-direction by means of corresponding ribs. Cushioning for ground reaction forces acting in the longitudinal direction (i.e., the Y-direction) of the shoe is not disclosed. In particular, the system does not provide any cushioning during ground contact with the heel.
It is, therefore, an object of the present invention to provide a cushioning element for a shoe sole that reduces loads on the muscles and the bones caused by multi-dimensional ground reaction forces, in particular during the first ground contact with the heel, thereby overcoming the above discussed disadvantages of the prior art.
The present invention relates to a sliding element for a shoe sole, in particular a sports shoe with an upper sliding surface and a lower sliding surface, wherein the lower sliding surface is arranged below the upper sliding surface so as to be slideable in at least two directions. A relative movement between the upper sliding surface and the lower sliding surface allows the foot to feel as if it is wearing a conventional shoe that contacts a surface with reduced friction, for example a soft forest ground. The sliding movement of the surfaces distributes the deceleration of the sole over a greater time period. This, in turn, reduces the amount of force acting on the athlete and the momentum transfer on the muscles and the bones.
The corresponding three-dimensional shapes of the upper and lower sliding surfaces make possible a multi-directional sliding movement between the upper and lower sliding surfaces. Complex multi-dimensional cushioning movements are possible, which are preferred during ground contact with the heel, rather than exclusive compression in the Z-direction.
In addition, a sliding element in accordance with the invention positively influences the moments and forces arising during running on cambered roads and during downhill running. A comparative study with conventional sole structures has shown that the sliding element allows measurable deflections, which noticeably reduce the loads arising during ground contact.
In one aspect, the invention relates to a sliding element for a shoe sole. The sliding element includes an upper sliding surface and a lower sliding surface. The lower sliding surface is arranged below the upper sliding surface, such as to be slideable in at least two directions.
In another aspect, the invention relates to a sole for an article of footwear. The sole includes a sliding element, which itself includes an upper sliding surface and a lower sliding surface. The lower sliding surface is arranged below the upper sliding surface, such as to be slideable in at least two directions.
In yet another aspect, the invention relates to an article of footwear including an upper and a sole. The sole includes a sliding element, which itself includes an upper sliding surface and a lower sliding surface. The lower sliding surface is arranged below the upper sliding surface, such as to be slideable in at least two directions.
In various embodiments of the foregoing aspects of the invention, the sliding element can include a spring element that is deflected by a sliding movement of the upper sliding surface relative to the lower sliding surface. The spring element can be pre-tensioned when the upper sliding surface and the lower sliding surface are in a neutral position and can include at least one elastic pin connecting the upper sliding surface to the lower sliding surface. An enlarged area may be included at each end of the elastic pin. Moreover, one enlarged end of the elastic pin may extend at least partially through an opening defined by the upper sliding surface and the other enlarged end of the pin may extend at least partially through an opening defined by the lower sliding surface. In one embodiment, the lower sliding surface is slideable relative to the upper sliding surface in at least three directions.
In another embodiment, the upper sliding surface forms a lower side of an upper heel cup and the lower sliding surface forms an upper side of a lower heel cup. The upper heel cup and the lower heel cup can include corresponding substantially spherical surfaces. In yet another embodiment, the sliding element can include a seal disposed at least partially about the upper sliding surface and the lower sliding surface to seal an intermediate space between the upper sliding surface and the lower sliding surface. Additionally, one of the sliding surfaces can include at least one projection for engaging a recess defined by the other sliding surface.
In still other embodiments, the upper heel cup can be coupled to a midsole of the sole and a separate heel sole unit may be coupled to the lower heel cup. The upper heel cup can extend along at least one of a medial and a lateral side into a midfoot area of the sole. The separate heel sole unit can include a midsole layer and an outsole layer.
In still another aspect, the invention relates to a cushioning system for an article of footwear. The cushioning system includes a ball joint disposed in at least one of a heel area and a forefoot area of the article of footwear. The ball joint includes at least a portion of a socket and at least a portion of a ball disposed at least partially within the socket, wherein the ball and socket are in slideable contact.
These and other objects, along with the advantages and features of the present invention herein disclosed, will become apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.